When logging measurement values it is very often decisive to relate measurement values of various process quantities in order to obtain evaluations based thereon. In this case, it happens frequently that measurement values have to be picked up at different locations, which are often spaced very far apart, and have to be transferred to a centralized location for storage. Using centralized storage allows for instance for a uniform data backup concept to be used for different measurement values. Furthermore, it is possible to make available only one evaluation infrastructure for treating all kinds of measurement results.
Conversion of the physical process information into measurement values, which can be evaluated by electronic data processing units, usually takes place at the measurement site. The field units convert the physical process information into numerical values, which must finally be forwarded to the centralized evaluator units.
Nowadays, transmission of process information from field units into a centralized database of an evaluator unit takes place e.g. via dialup connections, web servers integrated into field units, per email, SMS or by facsimile transmission. In all of these methods, in order to reach the measurement information, information has to be retrieved actively from a receiver. That is, measurement values are provided by the field unit at a location agreed upon, where they must then be fetched by the user, in particular by a subsequent processing instance.
In order to facilitate fetching, it is indeed possible to use polling procedures, which ensure that the information provided is interrogated and fetched at regular time intervals. However, with such polling procedures, or with fetching procedures triggered by the user, it is rather difficult to fetch information immediately after it has been logged. Especially with irregular measurement value logging, it may happen that the time interval between interrogation and provision of a measurement value is very long. Or it may happen that interrogation is done in intervals that are too short so that the measuring system is additionally loaded with frequent interrogation and performance thereof is impaired.